352 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 52. 



Diagram showing the variation in the number qfurosteges in specimens from San Francisco. 



d 



9 <? 



9 <? <? 



9 9 <? c? 9 c? 



99 99999 (?99 d d 



999 999999c?c?c?c?9<?<?c? <? 



66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 



Female: 



Male. 



Range of variation in 42 specimens: 



Males, 18 specimens 74 — 85 



Females, 24 specimens 66—80 



Further along when the table comparing these specimens with the 

 series from Sausalito is reviewed ; it will be noted that in both locali- 

 ties the range in the number of urosteges is from 66 to 85. These bare 

 figures fail to bring out one salient feature — the higher average that 

 exists in the Sausalito set. This difference may be seen at a glance if 

 the preceding and following diagrams be compared. 

 Diagram showing the variation in the number of urosteges in specimens from Sausalito. 



9 <? 



c? <? c? 



9 9 9 c? 



9 <? <? c? c? c? 9 



9 9999 99 <?(?c? <?c?<? (?c? 



66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 



Female. 



Male. 



Range of variation in 32 specimens: 



Males, 19 specimens 76 — 85 



Females, 13 specimens 66 — 85 



Over one-half of these from Sausalito have the tail docked, while 

 less than one-fifth of the snakes from Golden Gate Park are similarly 

 crippled. In grazing land this is frequently due to their being trod- 

 den upon by cattle. Where field rodents are plentiful the tail is often 

 bitten off and devoured by these animals. 



Variation in Preocular. 



The normal condition is a single preocular. Where two exist it is 

 due to the fragmentation of the lower one-third of the normal shield. 

 Wliere three are found it is due to a middle plate which has become 

 separated from the anterior superior shield. In the majority of speci- 

 mens the lower portion of the preocular is of a lighter tint and fre- 

 quently is indented at the margins. In the specimens showing varia- 

 tion in this character 25 per cent are males. 



Per cent. 



1 normal 92 



1-2 asymmetrical 4 



2 bilateral 2 



2-3 asymmetrical 2 



